1. Field of the Invention
This invention relates to apparatus and a method for the generation of a spiral gas stream in a pipeline, and apparatus and methods for the utilization of the spiral gas stream thus generated for the transportation of solid particles and for other purposes.
2. Description of the Prior Art
It has been widely applied for a long time in industry to transport particles of various solids, including coal, ore and cement, by gas stream in pipeline.
The fundamental principle of this transportation method is very simple: Pressurized gas is fed into a pipeline to form a high-speed gas stream, in which solid particles are suspended and transported to the outlet of the pipeline. To avoid settling of solid particles which may block the pipeline on the midway, it is necessary to keep the velocity of gas stream in the pipeline at high level. In general, solid particles of larger size and higher specific gravity require a higher velocity of gas stream than do smaller and lighter particles.
Consequently, the gas pressure at the inlet of the pipeline should be higher as the size and the specific gravity of the solid particles and the length of the pipeline increase. The gas pressure applied to high pressure pneumatic transportation system ranges usually from 2 to 7 Kg/cm.sup.2 G.
Several problems have been raised in this conventional pneumatic transportation system. The first problem is considerable wear of the inside wall of the pipeline due to collision of solid particles. When the velocity of gas stream is sufficient to transport solid particles of high specific gravity, the gas stream in pipeline forms a turbulent flow, and the solid particles suspended in that flow violently collide against the inside wall of the pipeline also under a turbulent condition, and if the solid particles are hard, the particles will wear the inside wall of the pipeline as sandblasting might and finally wear out the pipe wall. This phenomenon is remarkable especially in the region of bends in the pipeline.
Since this problem has been not yet effectively solved, it is inevitable to repair or exchange for new parts with a high frequency as high as once a month for the bending parts of a pipeline transporting pneumatically such hard solid particles as ore.
The second problem in the conventional pneumatic transportation system of solid particles by high-speed gas stream in a pipeline arises from the fact that a feeder for supplying solid particles into the pipeline is exposed to high gas pressure.
Usually, a screw conveyor is used as a feeder because a screw conveyor makes it easy to control quantitatively the amount of solid particles to be supplied, but from the structural point of view, a screw conveyor has an inefficient mechanism for sealing against gas pressure within the pipeline. Pressurizied gas at the inlet of the pipeline might blow back in the screw conveyor to form voids in the solid particles there. Not only do such voids lower the conveyor's supply efficiency and make it difficult to control the amount of solid particles to be supplied, but also the fine solid particles blown back into the conveyor enter into the bearings of rotating part in the screw conveyor causing rapid wear of the shafts and bearings. In addition, the hopper for feeding solid particles to the screw conveyor must be also air-tight. Consequently, when such a hopper becomes empty, it is necessary to interrupt the transportation of solid particles for the purpose of recharging it or to change over to another hopper.